1. Field of the Invention
The present invention relates to pharmaceutically active compounds and more particularly to pharmaceutical compositions that utilize or comprise one or more of such compounds. Preferred compounds are especially useful for the treatment or prophylaxis of undesired thrombosis. Also included are methods for treating thrombosis. The invention has a wide spectrum of applications including use in screening candidate compounds for the treatment or prophylaxis of thrombosis.
2. Background
Blood clotting assists hemostasis by minimizing blood loss. Generally, blood clotting is initiated by vessel damage and requires platelet aggregation, coagulation factors and inhibition of fibrinolysis. The coagulation factors act through a cascade that relates the vessel damage to formation of a blood clot (see generally L. Stryer, Biochemistry, 3rd Ed, W. H. Freeman Co., New York; and A. G. Gilman et al., The Pharmacological Basis of Therapeutics, 8th Edition, McGraw Hill Inc., New York, pp. 1311–1331).
Tissue factor (TF), an integral membrane protein of 263 amino acids, is responsible for initiating the coagulation protease cascade. Vascular damage exposes blood to tissue factor expressed on subendothelial cell surfaces, leading to the formation of a calcium-dependent, high-affinity complex with the plasma factor VII (FVII) or activated factor VII (FVIIa). Binding to TF promotes rapid proteolytic cleavage of the zymogen FVII to the active serine protease FVIIa by a number of proteases such as factor Xa, or thrombin. TF also functions as an essential cofactor for FVIIa by dramatically enhancing the catalytic efficiency of FVIIa for its protein substrates factors IX and X. TF/VIIa complex activates factors IX (FIX) and X (Fx) via limited proteolysis, ultimately leading to thrombin generation and fibrin deposition. Under pathological conditions such as atherosclerosis or following invasive surgical procedures such as microvascular graft, angioplasty, deployment of an implanted device (e.g., a stent, catheter or arteriovenous shunt), or endarterectomy, TF-initiated coagulation can lead to thrombotic disorders that can result e.g. in heart attack, stroke, unstable angina or other coronary disorder.
Thrombosis also may accompany various thromboembolic disorders and coagulopathies such as a pulmonary embolism (e.g., atrial fibrillation with embolization, deep vein thrombosis, etc.) and disseminated intravascular coagulation, respectively. Manipulation of body fluids can also result in an undesirable thrombus, particularly in blood transfusions or fluid sampling, as well as procedures involving extracorporeal circulation (e.g., cardiopulmonary bypass surgery) and dialysis.
Certain anti-coagulants have been used to alleviate or avoid blood clots associated with thrombosis. Blood clotting often can be minimized or eliminated by administering a suitable anti-coagulant or mixture thereof, including one or more of a coumarin derivative (e.g., warfarin and dicumarol) or a charged polymer (e.g., heparin, hirudin or hirulog). See e.g., Gilman et al, supra, R. J. Beigering et al., Ann. Hemathol., 72:177 (1996); J. D. Willerson, Circulation, 94:866 (1996).
Certain antibodies with anti-platelet activity have also been used to alleviate various thromboses. For example, ReoPro™ is a therapeutic antibody that is routinely administered to alleviate various thromboembolic disorders such as those arising from angioplasty, myocardial infarction, unstable angina and coronary artery stenoses. Additionally, ReoPro™ can be used as a prophylactic to reduce the risk of myocardial infarction and angina (J. T. Willerson, Circulation, 94:866 (1996); M. L. Simmons et al., Circulation, 89:596 (1994)).
However, use of prior anti-coagulants is often associated with side effects such as hemorrhaging, re-occlusion, “white-clot” syndrome, irritation, birth defects, thrombocytopenia and hepatic dysfunction. Long-term administration of anti-coagulants can particularly increase risk of life-threatening illness (see e.g., Gilman et al., supra).
Protein-based agents are potentially safer, but generally are limited to treatment of acute conditions and often are restricted to parenteral administration. Such agents are considered less suitable for long-term therapies for chronic diseases (such as atherosclerosis, a major cause of heart attack) due to the increased probability of immune response to a protein therapeutic, relatively high production cost and/or limited oral bioavailability.
It would thus be desirable to have new anti-coagulant agents. It would be particularly desirable to have new anti-coagulant agents that could be administered over a relatively long period to treat chronic conditions such as atherosclerosis.